Serotonin (5-HT) neurotransmission plays an important role in numerous physiological processes both in health and in psychiatric disorders. For example, 5-HT has been implicated in the regulation of feeding behavior. 5-HT is believed to work by inducing a feeling of fullness or satiety so eating stops earlier and fewer calories are consumed. It has been shown that a stimulatory action of 5-HT on the 5-HT2C receptor plays an important role in the control of eating and in the anti-obesity effect of d-fenfluramine. As the 5-HT2C receptor is expressed in high density in the brain (notably in the limbic structures, extrapyramidal pathways, thalamus and hypothalamus i.e. PVN and DMH, and predominantly in the choroid plexus) and is expressed in low density or is absent in peripheral tissues, a selective 5-HT2C receptor agonist can be a more effective and safe anti-obesity agent. Also, 5-HT2C knockout mice are overweight with cognitive impairment and susceptibility to seizure. Thus, the 5-HT2C receptor is recognized as a well-accepted receptor target for the treatment of obesity, psychiatric, and other disorders. See, for example, Halford et al., Serotonergic Drugs Effects on Appetite Expression and Use for the Treatment of Obesity, Drugs 2007; 67 (1): 27-55; Naughton et al., A Review Of The Role Of Serotonin Receptors In Psychiatric Disorders. Human Psychopharmacology (2000), 15(6), 397-415.
(R)-8-Chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (lorcaserin hydrochloride) is an agonist of the 5-HT2C receptor and shows effectiveness at reducing obesity in animal models and humans.
Various synthetic routes to (R)-8-chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine, its related salts, enantiomers, crystalline forms, and intermediates, have been reported in WO 2003/086306, WO 2005/019179, WO 2006/069363, WO 2007/120517, WO 2008/070111, and WO 2009/111004 each of which is incorporated herein by reference in its entirety.
Combinations of lorcaserin with other agents, including without limitation, phentermine, and uses of such combinations in therapy are described in WO 2006/071740, which is incorporated herein by reference in its entirety.
In December 2009, Arena Pharmaceuticals, Inc. submitted a New Drug Application, or NDA, for lorcaserin to the FDA. The NDA submission is based on an extensive data package from lorcaserin's clinical development program that includes 18 clinical trials totaling 8,576 patients. The pivotal phase 3 clinical trial program evaluated nearly 7,200 patients treated for up to two years, and showed that lorcaserin consistently produced significant weight loss with excellent tolerability. About two-thirds of patients achieved at least 5% weight loss and over one-third achieved at least 10% weight loss. On average, patients lost 17 to 18 pounds or about 8% of their weight. Secondary endpoints, including body composition, lipids, cardiovascular risk factors and glycemic parameters improved compared to placebo. In addition, heart rate and blood pressure went down. Lorcaserin did not increase the risk of cardiac valvulopathy. Lorcaserin improved quality of life, and there was no signal for depression or suicidal ideation. The only adverse event that exceeded the placebo rate by 5% was generally mild or moderate, transient headache. Based on a normal BMI of 25, patients in the first phase 3 trial lost about one-third of their excess body weight. The average weight loss was 35 pounds or 16% of body weight for the top quartile of patients in the second phase 3 trial.
In view of the growing demand for compounds useful in the treatment of disorders related to the 5-HT2C receptor, (R)-8-chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine has emerged has an important new compound. Accordingly, new and more efficient routes leading to intermediates useful in the preparation of (R)-8-chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine are needed. The processes and compounds described herein help meet these and other needs.